A semiconductor integrated circuit (IC) device, such as a processor, may include circuitry of many types of discrete circuit components, including transistors, resistors, and capacitors, as well as other components. Semiconductor IC manufacturers are subject to ever-increasing pressure to increase the speed (i.e. the clock rate) and performance of such IC devices while reducing package size and maintaining reliability. Thus, by way of example, a modern processor (e.g., general purpose microprocessors, digital signal processors, microcontrollers, etc.) may be implemented in a die that includes literally millions of closely spaced transistors and other discrete sub-micron components and operating at clock rates in the GHz range. As is well known, the power dissipation of a processor (and other IC devices) generally increases with operating frequency. As a result, these modern processors exhibit relatively high power dissipation. High power dissipation is generally undesirable and can be especially problematic in battery-powered applications.
One conventional technique to reduce power dissipation is “clock throttling”. Typical clock throttling techniques include reducing the frequency of a clock signal provided to selected units or subunits of the processor. Clock throttling tends to reduce the performance of the processor since the clock frequency is reduced even when the processor is trying to perform useful work. In addition, current clock throttling solutions are relatively coarse (i.e., take a relatively large number of clock cycles to enter the reduced clock frequency mode and to return to the normal clock frequency mode).
Another conventional technique is to reduce the supply voltage provided to the processor. The lower supply voltage tends to slow the switching speed of the transistors in the processor, which in turn tends to reduce the performance of the processor. In addition, the lower supply voltage may undesirable increase the processor's noise sensitivity. Further, like clock throttling, changing the supply voltage is a relatively coarse power conservation technique. This technique is widely used as an efficient way of reducing power dissipation as the power relates to the voltage in the power of three. For example, lowering the voltage by 20% would lower the power by 49%, while hurting the performance (clock rate) by only 20%. The limitation is that it takes many millions of clock cycles to stabilize a new voltage on an IC.
These clock throttling and voltage reduction techniques are commonly used in controlling the temperature of the processor and, thus, the aforementioned shortcomings are acceptable to prevent damage to the processor. However, for purely power conservation applications, these shortcomings may be unacceptable.